An example of a conventional article such as a surfboard is configured by a structure where an entire outer surface of urethane foam, which is a main body formed into the shape of the article, is coated and reinforced by FRP (Fiber Reinforced Plastics) (hereafter “first conventional technology”). Such a structure of urethane foam requires a predetermined strength, lightness in weight, and a degree of adhesion with the FRP.
Another example of conventional article such as a surfboard is configured by a structure where a hollow space is formed therein through a flow of urethane resin into a mold (hereafter “second conventional technology”), and such a structure is required to be light in weight, low in cost, and a variety of outer shape (various types of mold).
Further, in Japanese Laid-Open Publication number 2001-206286, it is disclosed a structure of surfboard established by reinforcing material called stringers within an inner space of a hollow structure where the stringer is attached to connect two inner facing surfaces along the longitudinal direction of the main body having the hollow structure.
Further, as a non-patent document 1, an article such as a surfboard with a hollow structure therein is introduced in a website on internet. For example, “Article Such as Hollow Carbon Fiber Surfboard” sold by a manufacturer “AVISO” is disclosed along with a cross sectional diagram showing its inner structure.
Moreover, as another non-patent document 2, “Salomon”, a large manufacturing and wholesale company of articles such as hollow surfboards, is manufacturing and selling a product called “S-CORE” as disclosed by its website.    Patent Document 1: Japanese Laid-Open Publication No. 2001-206286    Non-Patent Document 1: Website address that discloses the information on “AVISO”—http://www.nakisurf.com/faq/faq-board.html    Non-Patent Document 2: Home page address for “Salomon”—http://www.salomon.co.jp/index.html